Infection of the central nervous system (CNS) with the neurotropic murine coronavirus JHMV results in acute encephalomyelitis, primary demyelination , and persistent infection in susceptible strains. Complete elimination of virus during the acute infection by multiple effectors including CD8+ cytotoxic T lymphocytes (CTL), is critical in preventing viral persistence and chronic demyelination. We have recently shown that the absence of CD4+ T cells in JHMV infection results in decreased numbers of activated CTL in the brain and this is associated with a marked increase in the number of cells undergoing programmed cell death or apoptosis. As a direct extension of this work, we propose the general HYPOTHESIS that the infiltration and survival of CTL in CNS during JHMV infection is dependent, at least in part, upon CD4+ T cells. The first aim of the project will be to determine the mechanism by which CTL infiltrate into CNS tissue from the perivascular space and how this is modified by CD4+ cells. We suggest that CTL infiltration is increased by secretion of metalloproteinases (MMP-7, MMP-9) and in response to chemokine gradients (MIP-1alpha, RANTES) and that these processes are stimulated by the secreted products of CD4+ T cells. The second aim will be to determine the mechanism by which CTL undergo apoptosis in the CNS of JHMV-infected mice and how this is modulated by CD4+ T cells. We suggest apoptosis of CTL occurs secondary to deletion of the growth factor interleukin-2 (IL-2) OR by Fas-mediated killing, processes associated with decreased levels of bcl-2 and that CD4+ T cell depletion further accentuates IL-2 depletion. Both brains and isolated CTL from normal mice and CD4-deficient mice will be studied as well as specific mutant and transgenic strains. Pathogenesis will be altered by over expression of specific MMP, chemokines of apoptosis- related molecules using a Defective Interfering vector system. The results of these experiments will provide a better understanding of the mechanisms involved in CTL trafficking within the specialized microenvironment of the brain.